Although not exclusively, the present invention applies more particularly to a system which comprises a cockpit viewing screen, for example:                of ND (“Navigation Display”) type, that is to say a navigation screen which is used in a customary manner to present in flight the plot of the route desired for the airplane, that is to say which provides a graphical representation of the flight plan of the airplane and of the situation of the airplane on this flight plan; or        of OIT (“Onboard Information Terminal”) type, that is to say an onboard information screen which is multifunctional and which is in particular used to display the electronic documentation of the airplane.        
Within the framework of the present invention, the system for assisting airport navigation is of the type comprising:                at least one means for determining the current position of the airplane;        at least one cartographic database of the airport in which said airplane is situated; and        a display device comprising at least one cockpit viewing screen which is capable of displaying a display mode at least of a first type, for which said cockpit viewing screen presents at least:                    an airplane symbol which illustrates said current position of the airplane and which is fixed at a predetermined centered position; and            a part of a map which represents at least partially the airport in which said airplane is situated. Said map part is mobile and tied to the motion of the airplane so as to move with respect to said fixed airplane symbol in conformity with the current position of the airplane in said airport, according to a standard display.                        
In a customary manner, a display mode of the aforesaid first type can be a customary mode termed arc or a customary mode termed rose.
Generally, a cockpit viewing screen is also capable of displaying a display mode of a second type, termed plan mode, for which the cockpit viewing screen presents at least one auxiliary map part which is fixed and an auxiliary symbol (illustrating the current position of the airplane) which is mobile. Such a plan mode makes it possible moreover for an operator, in particular the pilot of the airplane, to move the map part displayed in the direction and by the amplitude that he desires. Such a free movement is not possible in the arc and rose modes, since in these two cases the display is kept centered on the airplane symbol which is fixed.
Now, in the course of airport navigation, the pilot is often required to consult information which is far removed from the current position of the airplane, for example to prepare for taxiing or to anticipate maneuvers. Such a consultation is easily achievable in plan mode, since it suffices in this case for the pilot to move the map to display the part of the airport in which he is interested.
On the other hand, in arc mode and in rose mode, if the pilot has to consult information which is situated at a distance from the airplane greater than that displayed in accordance with the selected scale of the display mode, he has:                either to modify this scale so as to display a more significant zone of the airport, thereby, however, causing him to lose significant information since the displayed level of details is dependent on the scale selected;        or to switch to plan mode so as to carry out the consultation, which is, however, neither recommended nor acceptable during airport navigation, since the display is then no longer centered on the airplane so that the system no longer adequately fulfills its principal function of assisting navigation.        